In 1936, shortly after the outbreak of the Spanish Civil War, the moribund philosopher Miguel de Unamuno, author of the classic existential text Tragic Sense of Life, died alone in his office of heart failure at the age of 72.

Unamuno was no religious sentimentalist. As a rector and Professor of Greek at the University of Salamanca, he was an advocate of rationalist ideals and even died a folk hero for openly denouncing Francisco Franco's fascist regime. He was, however, ridden with a 'spiritual' burden that troubled him nearly all his life. It was the problem of death. Specifically, the problem was his own death, and what, subjectively, it would be "like" for him after his own death: "The effort to comprehend it causes the most tormenting dizziness." I've taken to calling this dilemma "Unamuno's paradox" because I believe that it is a universal problem. It is, quite simply, the materialist understanding that consciousness is snuffed out by death coming into conflict with the human inability to simulate the psychological state of death.

Of course, adopting a parsimonious stance allows one to easily deduce that we as corpses cannot experience mental states, but this theoretical proposition can only be justified by a working scientific knowledge (i.e., that the non-functioning brain is directly equivalent to the cessation of the mind). By stating that psychological states survive death, or even alluding to this possibility, one is committing oneself to a radical form of mind-body dualism. Consider how bizarre it truly is: Death is seen as a transitional event that unbuckles the body from its ephemeral soul, the soul being the conscious personality of the decedent and the once animating force of the now inert physical form. This dualistic view sees the self as being initially contained in bodily mass, as motivating overt action during this occupancy, and as exiting or taking leave of the body at some point after its biological expiration. So what, exactly, does the brain do if mental activities can exist independently of the brain? After all, as John Dewey put it, mind is a verb, not a noun.

And yet this radicalism is especially common. In the United States alone, as much as 95% of the population reportedly believes in life after death. How can so many people be wrong? Quite easily, if you consider that we're all operating with the same standard, blemished psychological hardware. It's tempting to argue, as Freud did, that it's just people's desire for an afterlife that's behind it all. But it would be a mistake to leave it at that. Although there is convincing evidence showing that emotive factors can be powerful contributors to people's belief in life after death, whatever one's motivations for rejecting or endorsing the idea of an immaterial soul that can defy physical death, the ability to form any opinion on the matter would be absent if not for our species' expertise at differentiating unobservable minds from observable bodies.

But here's the rub. The materialist version of death is the ultimate killjoy null hypothesis. The epistemological problem of knowing what it is "like" to be dead can never be resolved. Nevertheless, I think that Unamuno would be proud of recent scientific attempts to address the mechanics of his paradox. In a recent study, for example, I reported that when adult participants were asked to reason about the psychological abilities of a protagonist who had just died in an automobile accident, even participants who later classified themselves as "extinctivists" (i.e., those who endorsed the statement "what we think of as the 'soul,' or conscious personality of a person, ceases permanently when the body dies") nevertheless stated that the dead person knew that he was dead. For example, when asked whether the dead protagonist knew that he was dead (a feat demanding, of course, ongoing cognitive abilities), one young extinctivist's answer was almost comical. "Yeah, he'd know, because I don't believe in the afterlife. It is non-existent; he sees that now." Try hard as he might to be a good materialist, this subject couldn't help but be a dualist.

How do I explain these findings? Like reasoning about one's past mental states during dreamless sleep or while in other somnambulistic states, consciously representing a final state of non-consciousness poses formidable, if not impassable, cognitive constraints. By relying on simulation strategies to derive information about the minds of dead agents, you would in principle be compelled to "put yourself into the shoes" of such organisms, which is of course an impossible task. These constraints may lead to a number of telltale errors, namely Type I errors (inferring mental states when in fact there are none), regarding the psychological status of dead agents. Several decades ago, the developmental psychologist Gerald Koocher described, for instance, how a group of children tested on death comprehension reflected on what it might be like to be dead "with references to sleeping, feeling 'peaceful,' or simply 'being very dizzy.'" More recently, my colleague David Bjorklund and I found evidence that younger children are more likely to attribute mental states to a dead agent than are older children, which is precisely the opposite pattern that one would expect to find if the origins of such beliefs could be traced exclusively to cultural learning.

It seems that the default cognitive stance is reasoning that human minds are immortal; the steady accretion of scientific facts may throw off this stance a bit, but, as Unamuno found out, even science cannot answer the "big" question. Don't get me wrong. Like Unamuno, I don't believe in the afterlife. Recent findings have led me to believe that it's all a cognitive illusion churned up by a psychological system specially designed to think about unobservable minds. The soul is distinctly human all right. Without our evolved capacity to reason about minds, the soul would never have been. But in this case, the proof isn't in the empirical pudding. It can't be. It's death we're talking about, after all.